From ebc9baed42e42f9b51cf61672b7afb72f068d523 Mon Sep 17 00:00:00 2001 From: Peter Hurley Date: Mon, 11 Mar 2013 16:44:40 -0400 Subject: [PATCH] tty: Separate release semantics of ldisc reference tty_ldisc_ref()/tty_ldisc_unref() have usage semantics equivalent to down_read_trylock()/up_read(). Only callers of tty_ldisc_put() are performing the additional operations necessary for proper ldisc teardown, and then only after ensuring no outstanding 'read lock' remains. Thus, tty_ldisc_unref() should never be the last reference; WARN if it is. Conversely, tty_ldisc_put() should never be destructing if the use count != 1. Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman --- drivers/tty/tty_ldisc.c | 69 +++++++++++++++++++++-------------------- 1 file changed, 35 insertions(+), 34 deletions(-) diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c index 328ff5b544a5..9362a1030c95 100644 --- a/drivers/tty/tty_ldisc.c +++ b/drivers/tty/tty_ldisc.c @@ -49,37 +49,6 @@ static inline struct tty_ldisc *get_ldisc(struct tty_ldisc *ld) return ld; } -static void put_ldisc(struct tty_ldisc *ld) -{ - unsigned long flags; - - if (WARN_ON_ONCE(!ld)) - return; - - /* - * If this is the last user, free the ldisc, and - * release the ldisc ops. - * - * We really want an "atomic_dec_and_raw_lock_irqsave()", - * but we don't have it, so this does it by hand. - */ - raw_spin_lock_irqsave(&tty_ldisc_lock, flags); - if (atomic_dec_and_test(&ld->users)) { - struct tty_ldisc_ops *ldo = ld->ops; - - ldo->refcount--; - module_put(ldo->owner); - raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags); - - kfree(ld); - return; - } - raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags); - - if (waitqueue_active(&ld->wq_idle)) - wake_up(&ld->wq_idle); -} - /** * tty_register_ldisc - install a line discipline * @disc: ldisc number @@ -363,13 +332,45 @@ EXPORT_SYMBOL_GPL(tty_ldisc_ref); void tty_ldisc_deref(struct tty_ldisc *ld) { - put_ldisc(ld); + unsigned long flags; + + if (WARN_ON_ONCE(!ld)) + return; + + raw_spin_lock_irqsave(&tty_ldisc_lock, flags); + /* + * WARNs if one-too-many reader references were released + * - the last reference must be released with tty_ldisc_put + */ + WARN_ON(atomic_dec_and_test(&ld->users)); + raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags); + + if (waitqueue_active(&ld->wq_idle)) + wake_up(&ld->wq_idle); } EXPORT_SYMBOL_GPL(tty_ldisc_deref); +/** + * tty_ldisc_put - release the ldisc + * + * Complement of tty_ldisc_get(). + */ static inline void tty_ldisc_put(struct tty_ldisc *ld) { - put_ldisc(ld); + unsigned long flags; + + if (WARN_ON_ONCE(!ld)) + return; + + raw_spin_lock_irqsave(&tty_ldisc_lock, flags); + + /* unreleased reader reference(s) will cause this WARN */ + WARN_ON(!atomic_dec_and_test(&ld->users)); + + ld->ops->refcount--; + module_put(ld->ops->owner); + kfree(ld); + raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags); } /** @@ -1001,7 +1002,7 @@ void tty_ldisc_init(struct tty_struct *tty) */ void tty_ldisc_deinit(struct tty_struct *tty) { - put_ldisc(tty->ldisc); + tty_ldisc_put(tty->ldisc); tty_ldisc_assign(tty, NULL); } -- 2.20.1